Due to its unique structure and amazing physicochemical properties including high chemical inertness, large specific surface area, high electric conductivity, mechanical flexibility, and biocompatibility, graphene holds great potential for bioelectronic implants.
One of the prominent uses of graphene in bioelectronics is recording of electrical signals from body parts, such as the heart or brain. Last year’s edition of the largest medical trade fair in the world – MEDICA 2017, featured several exhibits using graphene in biomedicine. Among the exhibits were a brain activity detector for early warning of epileptic seizures, a retinal implant serving as optical prostheses for people who have lost their sight, a brain-computer interface containing graphene electrodes to measure brain activity, and a fully functional robotic hand controlled by a bracelet with graphene sensors.
Illustration: Graphene ocular implants. Source: Graphene transistors for bioelectronics (arXiv)
Preceding these successful demonstrations of technology were years of painstaking scientific research, that bit-by-bit explored the possibilities and advantages of using graphene for bioelectronics. Early work focused on quantifying the interaction of graphene with biological material, such as lipid membranes. It was evident that the addition of tiny amounts of biological material to the surface of graphene would change its properties, i.e. graphene would behave as a biosensor. The most common graphene device used in biosensing is the graphene field effect transistor – GFET. GFET array sensor platforms have also been used to identify malaria-infected red blood cells at the individual cell resolution. Subsequent work showed that one can grow live cells on graphene and monitor their chemical activity via accompanying electrical signals. Both intracellular and extracellular activity was detected, such as cellular excretion and cell membrane’s potential modulation.
Other than serving the important function of registering biological signals, graphene found surprising new applications such as in bone implants. Porous solids made of graphene oxide were found to possess similar mechanical properties and biocompatibility to titanium, a standard bone-replacement material. Using graphite molds, this new material can be shaped into custom complex shapes as desired. And although eyebrows were initially raised about the heat that emanates when power is provided to graphene implants, which could damage the host organism, researchers quickly found a solution to overheating – adding water between graphene and the biological material. A thin layer of water separating the graphene from tissue could save surrounding cells from being fried when an implant is operated.
Taking on the offensive, latest research shows that a layer of vertical graphene flakes on a surface kill harmful bacteria, potentially stopping infections during procedures such as implant surgery. While destroying bacteria, the sharp graphene flakes do not damage human cells because a bacterium is one micrometer in diameter while a human cell is 25 micrometers.To conclude, graphene is an excellent material for bioelectronics, proven by countless research papers that affirm this application as well as some recent working graphene implant prototypes. Graphene bioelectronics are among the most promising applications of graphene field effect transistors (GFETs), which are driving the growth of the single-layer graphene market.